1. Field of the Invention
This invention relates to components for office chairs and more particularly relates to a blow molded, back-filled cushion product and process for making the product.
2. Background Information
Presently office chair components such as armrests are made in three different ways. These methods involve a polyurethane self-skin foam, an injection molded PVC cover assembled with foam, and an injection molded PVC skin filled with foam. These arms are always mounted to a substrate or chair bracket that is mounted to the under side of a seat pan. These standard armrest substrates or mounting brackets are sold in large quantifies to small and mid-size chair manufacturers.
The polyurethane self-skin foam is a very common method because the tooling is not expensive, and the part can be made on a wide variety of substrates. This allows companies to make standard armrest shapes that can be sold as open, off-the-self items to a wide variety of customers. Since the tooling investment is low, some small and mid-market chair manufacturers design and tool their own self-skin part. The disadvantage of self-skin parts is that by nature they are very hard, and difficult to make in colors.
It is generally agreed in the marketplace that a PVC skin and foam combination is more desirable due to the durability of the skin, and the ability to use a soft foam behind it. On average, a PVC skin can be up to 30% softer than a self-skin armrest.
Injection molded product skins need to have a large enough opening to extract it from the tool. The large opening at the bottom of the part due to the product skin shape must be covered in a way that traps the skin so it cannot be pulled off a chair arm by an end user when mounted on a chair. Large manufacturers of office chairs with large tooling budgets solve this problem by designing a substructure to trap the skin. Even with this design the skin frequently is damaged by being pulled loose by an end user.
Small and mid-size companies that cannot afford to tool their own substrates, buy standard substrates. A mating piece and staples are needed to trap and secure the skin so that it cannot be pulled off and to act as an interface between the arm and the substrate. The expense to create both a tool for a PVC skin and mating piece, along with the costs of the part make it extremely prohibitive for a small to mid-market chair manufacturer to use PVC. In fact, there does not appear to be any standard off-the-shelf PVC skin armrest existing in the marketplace today.
It is therefore one object of the present invention to provide a way to make a PVC and resilient foam armrest without a large opening eliminating the need for a mating piece, yet retaining all the benefits of a PVC and foam chair component or armrest.
Another object of the present invention is to provide a method for making a skin for a chair component such as an armrest that is initially a completely sealed enclosure.
Still another object of the present invention is to create a skin to make an armrest using a blow molding process that allows this manufacturer of a skin that is completely enclosed and as a result cannot be pulled off by the end user and needs no mating piece.
Still another object of the present invention is to provide a method for manufacturing a skin to produce an armrest that can be mounted to virtually any standard armrest bracket or substrate.
Still another object of the present invention is to provide a method for making a skin to produce an armrest that can reduce the cost to tool the skin by as much as 85% over an injected molded PVC skin reducing capitol outlay that is much more acceptable to small and mid-market companies.
The purpose of the present invention is to provide a process for making a cushioned product for chairs such as armrests at substantially reduced cost and with an improved cushioned construction.
It was discovered that an improved product at substantially reduced cost can be manufactured by using a blow molded, backfilled cushioned process. Blow molding is a primary method to form hollow plastic objects such as containers. The process includes clamping the ends of a softened tube polymers which can either be extruded or reheated, inflating a polymer against molded walls, and cooling the product before removing it from the mold.
The manufacture of the present cushioned product involves using a PVC material with ultraviolet (UV) inhibitors, fire retardant and a soft durometer formulation that is loaded into a blow molding machine. The polyvinyl chloride (PVC) material is heated sufficiently to melt the product. The machine gravity feeds an extruded cylinder of material called a preform. The thickness of the walls of the extrusion is regulated by the machine. For the purposes of an armrest, a wall thickness of approximately nine one-hundredths of an inch (0.090xe2x80x3) is desired.
The tool has the shape of an armrest and is clamped around extruded PVC material and air is blown into the cylinder by the machine. The process of blowing air while clamping the tool around the cylinder makes the PVC material take the shape of the armrest formed by the mold cavity. The force and direction of the air is determined by the shape of the skin. This produces a sealed hollow enclosure in the shape of the armrest with a recess about one-half to two-thirds the surface area along one side. The part is then extracted from the tool and excess material is trimmed or by any suitable arrangement with a sharp knife.
The tools used to make the skin by blow molded process are machined preferably out of steel or aluminum. The interior surface or cavity in the tool is then etched with the texture of the finished part desired. Small vent holes are usually drilled into specific locations in the tool. Air is drawn through these holes at the same time air is blown into the tool resulting in a xe2x80x9cvacuumxe2x80x9d that helps press the skin firmly against the walls of the tool.
Since the skin and the backfilling foam for the armrest do not provide any substantial structural integrity, a rigid insert or arm bracket adapter is used. The rigid insert is installed in the hollow enclosure in the shape of the armrest through holes cut in the recess formed in the enclosure. Preferably the insert or adapter can be of any suitable rigid material such as wood, steel, aluminum but is preferably of a synthetic plastic. The insert provides a bracket adapter having a rigid structure used to attach the armrest to the chair bracket and gives structural integrity to the product. The hole cut in the recess on the underside of the hollow enclosure forming the skin is just large enough to squeeze the rigid insert inside the skin.
The part is finished by using an epoxy tool constructed to mirror the outside shape of the hollow enclosure forming the skin for the armrest. The rigid insert or adapter is attached to one half of the epoxy tool via a press fit or by a screw threads. The epoxy tool mold is then closed trapping the hollow enclosure forming the skin and the insert in the tool which insures that foam stays inside the PVC skin.
Foam is then injected through an aperture in the insert behind the insert into the hollow skin which expands as it takes the shape of the skin and the tool. Preferably the foam is a type that provides a suitably resilient armrest. The hollow enclosure forming the skin is filled with the foam which acts to press the rigid insert against the recess in the enclosure providing a sealed product. The rigid insert also has a peripheral ridge or shoulder that mates with a peripheral wall of the recess providing a secure fit between the PVC skin and the rigid insert.
The rigid bracket adapter is also provided with threaded holes for attaching the product to chair brackets or substrates. When an armrest is formed in this manner, the rigid insert provides two mounting holes for mounting the armrest on a chair bracket. Also preferably, the apertures cut out of the recess in the hollow enclosure forming the skin are three separate apertures leaving two webs of material to improve the integrity of the skin.